I would like to describe my vision of what a protection board should be like for lithium-ion batteries of various chemistries and different capacities. Now, of course, there is a very large selection of different BMS for li-ion batteries. But simple BMSs have strict and overly critical response settings, which often causes batteries to fail (mostly they swell from overcharging). But advanced BMS, which have many components and are able to measure even the internal resistance of cells, and configure and exchange data via a PC and the Internet, are still very expensive, and due to their complexity they are difficult to use for ordinary people, and their cost is high .
I think now the biggest problem in using high-capacity lithium-ion batteries is the monitoring and protection systems for such batteries. I repeat, there are already solutions, but they can be counted on one hand, and they are expensive and not entirely universal, although progress in this direction does not stand still.
The word BMS itself means Battery Monitoring System that is, a battery monitoring system, and this short designation can refer to both simple analog protection boards and complex micro-computer monitoring systems for lithium-ion batteries. But as I already wrote above, the first ones are too primitive and have too critical trigger settings, and the second ones are too sophisticated and expensive. But there is no such thing battery monitoring system, which would be cheap and simple, but at the same time could be customized for different types li-ion batteries, as well as charge/discharge cutoff settings and balancing settings.
Photos of lithium-ion battery protection boards
BMS for lifepo4
This photo shows a simple and cheap protection board for lifepo4 batteries 4s 12v (4 cells). These BMSs are usually installed inside batteries, such as power tool batteries.BMS protection boards can be of different sizes and for different numbers of cells, that is, individual batteries. The operating principle of such boards is very simple; they monitor the voltage on each battery cell. And if the voltage in any cell exceeds the operating threshold, then the power transistors in the BMS will operate and disconnect the battery from the charger or consumers. Also, when the voltage is set, balancing is activated. The main parameter that you should pay attention to is the current for which the protection board is designed.
Below in the photo is a more expensive and fully functional BMS
BMS
There are also full-fledged BMSs that can be configured and display all battery data on a PC. They also have an additional LCD display to display the current battery statusThere are also other types of BMS, for example those aimed at working as part of a solar power plant, and they can also be used in electric transport.
BMS
Controller for lithium-ion batteries with full control of cell status and status display on PC and LCD display
Well, another example of a BMS created for electric vehicles
BMS for electric vehicle
Controller and monitoring of lithium-ion batteries for electric vehicles
Advantages and disadvantages of various BMS
Cheap analog protection boards are mainly intended for electric vehicles and power tools, and have critical protection and balancing thresholds, so they cannot operate in buffer mode and still balance the cells. This leads to an imbalance and frequent activation of the protection and overcharging of the cells. And expensive BMS can do everything, but they are very expensive, in my opinion, and are designed for large capacities, and for a small-capacity battery, these BMS will cost more than the battery itself.My BMS concept
1. I think it is quite enough to control the cells and the battery as a whole only by voltage, without complicating it with additional current and resistance measurements. Yes, of course, to accurately determine the capacitance and currents passing in the circuit, I would like to know everything. But the average user is not at all interested in what currents wander between the cells, their internal resistance, or simply the charge/discharge current. And the charging current is usually shown by the controllers through which the battery is charged. And if not, then you can install an ammeter separately. I think that apart from measuring the voltage, you don’t need to measure anything else, and from it you can quite accurately see the condition of the battery and individual cells.2. I’m still thinking absolutely unnecessary temperature sensors, since these are extra wires if the protection board is not installed on the battery. Well, overheating of the battery can occur at huge charge/discharge currents, which usually never happens. Typically, batteries are charged and discharged with small currents relative to the capacity, and let’s say a battery with a capacity of 100Ah, no one will charge with a current of 300-500A and discharge with such currents. Therefore, overheating with working cells is simply impossible.
3. Battery protection board is required should be able to be configured for different types of li-ion Battery, and balancing threshold settings. And for this, a display and control buttons must be installed. Of course, now you can easily connect to a PC and work with settings through software. But this is not convenient since a PC is not always at hand, and it is easier to see what is happening and configure it directly on the BMS than to connect to a PC, especially since not all are confident PC users. In general, I am for a good and large display on the BMS itself, but communication with a PC and monitoring with log recording is simply useless.
4. The work setup should be as follows: Setting the voltage threshold at which the charger turns off. For example, for lifepo4 it is 3.6-3.9 volts per cell. In this case, the shutdown threshold must be manually changed and any value must be specified, at least 3.40 volts, at least 4.30 volts, that is, for any type of lithium-ion batteries. And for working in buffer mode, where the battery is constantly under voltage and a 100% constant charge has a detrimental effect on the cells (they swell).
In this case, the board does not need built-in power switches to open the contact. In general, charge and discharge need to be divided into two separate channels, so that when the charger is disconnected from the battery, consumers do not find themselves in a situation where the battery is disconnected and they are powered only by the charger. And the charger can be solar panels, a wind generator, or any other source with unstable and high voltage, from which connected consumers can burn out without a battery. To prevent this from happening (as has already happened), it is necessary to separate the channels for disconnecting charging and consumers.
At the same time, there is no need to install transistor switches on the board for a certain current, since for some, say, 10A is enough, and for others, 200A is not enough. Instead of keys, you can simply make low-power terminals, say, with a current of 1A, on which you can hang regular or solid-state relays, which can be used to turn off charging and consumers. For example, if your charging current does not exceed 20A, then we set a 20A relay to charge. And if the discharge through the inverter occurs with currents up to 100A, then set the consumer disconnect relay to 100A.
5. Cell balancing thresholds must also be adjusted and the balancing current should be quite powerful, I think up to 5A in case of using low-quality cells with different internal resistance and different capacities. This is where you can use PWM technology to set the balancing current. Or, for example, make it possible to change balancing resistors for different currents.
Appearance of the li-ion battery controller
In appearance, I want to see something like this device. Same with the display, only three times larger, totaling 4-5 inches.BMS lcd
Li-ion battery controllerThe BMS should also have outputs to the cells, only on bolts, I think the number is any from 2S to 16S. The charger shutdown output for an external shutdown relay, and the consumer shutdown output is similar. And I think nothing more is needed. And since the balancers will be located inside the BMS, there must be a massive aluminum radiator capable of dissipating up to 300 watts of energy.
In general, of course, you can make complete BMSs with internal switches and different balancing currents, and for different numbers of cells, but they will need to be produced in dozens of different configurations. And so there is one BMS suitable for the main tasks. The balancing current of 5A per cell is of course too high, since with 16 cells and the operation of all balancers, the power dissipated into heat will be up to 300 watts. But as I described above, the balancing current can be set. Well, in order to reduce the dimensions and the radiator, the maximum balancing current can be reduced by 5 times. 1A I think will also be enough even for a large capacity battery.
That's all, I think I explained in detail what I would like to see and why this is so...
There hasn't been a review of converting a screwdriver to lithium for a long time :)
The review is mainly devoted to the BMS board, but there will be links to some other little things involved in converting my old screwdriver to 18650 lithium batteries.
In short, you can take this board; after a little finishing, it works quite well in a screwdriver.
PS: a lot of text, pictures without spoilers.
P.S. The review is almost an anniversary on the site - the 58000th, according to the address bar of the browser;)
What is this all for
I have been using a nameless two-speed 14.4 volt screwdriver, bought cheaply at a construction store for several years now. More precisely, not just completely nameless - it bears the brand of this construction store, but not some famous one either. Surprisingly durable, it hasn’t broken yet and does everything I ask of it - drilling, tightening and unscrewing screws, and working like a winder :)
But his native NiMH batteries did not want to work for so long. One of the two complete ones finally died a year ago after 3 years of operation, the second recently no longer lived, but existed - a full charge was enough for 15-20 minutes of operation of the screwdriver with interruptions.
At first I wanted to do it with little effort and simply replace the old cans with the same new ones. I bought these from this seller -
They worked great (albeit a little worse than their original counterparts) for two or three months, after which they died quickly and completely - after a full charge they were not even enough to tighten a dozen screws. I don’t recommend taking batteries from him - although the capacity initially corresponded to what was promised, they did not last long.
And I realized that I would still have to bother.
Well, now about the main thing :)
Having chosen Ali from the offered BMS boards, I settled on the one under review, based on its dimensions and parameters:- Model: 548604
- Overcharge cutoff at voltage: 4.28+ 0.05 V (per cell)
- Recovery after overcharge shutdown at voltage: 4.095-4.195V (per cell)
- Over-discharge voltage cut-off: 2.55±0.08 (per cell)
- Overcharge shutdown delay: 0.1s
- Temperature range: -30-80
- Short circuit shutdown delay: 100ms
- Overcurrent shutdown delay: 500 ms
- Cell balancing current: 60mA
- Working current: 30A
- Maximum current (protection trip): 60A
- Short circuit protection operation: self-healing after load disconnection
- Dimensions: 45x56mm
- Main functions: overcharge protection, overdischarge protection, short circuit protection, overcurrent protection, balancing.
All board components are placed on one side: 
The second side is empty and covered with a white mask: 
The part responsible for balancing during charging: 
This part is responsible for protecting cells from overcharge/overdischarge and it is also responsible for general protection against short circuit: 
Mosfets: 
It is assembled neatly, there are no obvious flux stains, the appearance is quite decent. The kit included a tail with a connector, which was immediately plugged into the board. The length of the wires in this connector is about 20-25 cm. Unfortunately, I didn’t take a picture of it right away.
What else did I order specifically for this alteration:
Batteries -
Nickel strips for soldering batteries: (yes, I know that you can solder with wires, but the strips will take up less space and will be more aesthetically pleasing :)) And initially I even wanted to assemble contact welding (not only for this alteration, of course), that’s why I ordered the strips, but laziness prevailed and I had to solder them.
Having chosen a free day (or rather, having blatantly sent all other matters away), I set about redoing it. To begin with, I disassembled the battery with dead Chinese batteries, threw out the batteries and carefully measured the space inside. Then I sat down to draw the battery holder and circuit board in a 3D editor. I also had to draw the board (without details) in order to try on everything assembled. It turned out something like this: 
According to the idea, the board is attached from above, one side into the grooves, the other side is clamped with an overlay, the board itself lies in the middle on a protruding plane so that when it is pressed it does not bend. The holder itself is made of such a size that it fits tightly inside the battery case and does not dangle there.
At first I thought about making spring contacts for batteries, but abandoned this idea. This is not the best option for high currents, so I left cutouts in the holder for nickel strips with which the batteries will be soldered. I also left vertical cutouts for the wires, which should extend from the inter-can connections beyond the lid.
I set it to be printed on a 3D printer from ABS and after a few hours everything was ready :) 
When screwing everything on, I decided not to trust screws and fused these M2.5 plug-in nuts into the body: 
Got it here -
Great item for this type of use! It is fused slowly with a soldering iron. To prevent the plastic from packing inside when melting into blind holes, I screwed a bolt of suitable length into this nut and heated its head with a soldering iron tip with a large drop of tin for better heat transfer. The holes in the plastic for these nuts are left slightly smaller (0.1-0.2 mm) than the diameter of the outer smooth (middle) part of the nut. They hold very tightly, you can screw in and unscrew the bolts as much as you like and don’t be too shy with the tightening force.
In order to have the possibility of cell-by-can control and, if necessary, charging with external balancing, a 5-pin connector will stick out in the back wall of the battery, for which I quickly threw on a scarf and made it on the machine: 
The holder has a platform for this scarf.
As I already wrote, I soldered the batteries with nickel strips. Alas, this method is not without its drawbacks, and one of the batteries was so outraged by this treatment that it left only 0.2 volts on its contacts. I had to desolder it and solder another one, fortunately I took them with a reserve. Otherwise there were no difficulties. Using acid, we tin the battery contacts and nickel strips cut to the required length, then thoroughly wipe everything tinned and around it with cotton wool and alcohol (but you can also use water), and solder it. The soldering iron must be powerful and either be able to react very quickly to the tip cooling, or simply have a massive tip that will not cool instantly upon contact with a massive piece of iron.
Very important: during soldering and during all subsequent operations with the soldered battery pack, you must be very careful not to short-circuit any battery contacts! In addition, as indicated in the comments ybxtuj, it is very advisable to solder them discharged, and I absolutely agree with him, this way the consequences will be easier if something does short out. A short circuit of such a battery, even a discharged one, can lead to big troubles.
I soldered wires to three intermediate connections between the batteries - they will go to the BMS board connector for monitoring the banks and to the external connector. Looking ahead, I want to say that I did a little extra work with these wires - they can not be led to the board connector, but soldered to the corresponding pins B1, B2 and B3. These pins on the board itself are connected to the connector pins. 
By the way, I used silicone insulated wires everywhere - they do not react to heat at all and are very flexible. I bought several sections on Ebay, but I don’t remember the exact link... I really like them, but there is a minus - silicone insulation is not very mechanically strong and is easily damaged by sharp objects.
I tried on the batteries and the board in the holder - everything is excellent: 
I tried on a handkerchief with a connector, used a Dremel to cut out a hole in the battery case for the connector... and missed the height and took the size from the wrong plane. The result was a decent gap like this: 
Now all that remains is to solder everything together.
I soldered the included tail onto my scarf, cutting it to the required length: 
I also soldered the wires from the inter-can connections there. Although, as I already wrote, it was possible to solder them to the corresponding contacts of the BMS board, there is also an inconvenience - in order to remove the batteries, you will need to unsolder not only the plus and minus from the BMS, but also three more wires, but now you can simply pull out the connector.
I had to tinker a little with the battery contacts: in the original version, the plastic part (holding the contacts) inside the battery leg is pressed by one battery standing directly under it, but now I had to think about how to fix this part, so as not to be tight. Here's the detail: 
In the end, I took a piece of silicone (left over from pouring some form), cut off a roughly suitable piece from it and inserted it into the leg, pressing that part. At the same time, the same piece of silicone presses the holder with the board, nothing will dangle.
Just in case, I laid Kapton insulating tape over the contacts, and grabbed the wires with a few snot drops of hot glue so that they would not get between the halves of the case when assembling it. 
Charging and balancing
I left the original charger from the screwdriver, it just produces about 17 volts at idle. True, charging is stupid and there is no current or voltage stabilization in it, there is only a timer that turns it off about an hour after the start of charging. The current output is about 1.7A, which, although a bit too much, is acceptable for these batteries. But this is until I complete it to normal, with stabilization of current and voltage. Because now the board refuses to balance one of the cells, which initially had a charge of 0.2 volts more. The BMS turns off the charge when the voltage on this cell reaches 4.3 volts, respectively, on the rest it remains within 4.1 volts.I read somewhere a statement that this BMS normally balances only with CV/CC charging, when the current gradually decreases at the end of the charge. Perhaps this is true, so charging upgrades await me ahead :)
I haven’t tried to discharge it completely, but I’m sure that the discharge protection will work. There are videos on YouTube with tests of this board, everything works as expected.
And now about the rake
All banks are charged to 3.6 volts, everything is ready to start. I insert the battery into the screwdriver, pull the trigger and... I’m sure that more than one person familiar with this rake now thought, “And the hell started your screwdriver” :) Absolutely right, the screwdriver twitched slightly and that’s it. I release the trigger, press again - the same thing. I press it smoothly - it starts and accelerates, but if you start it a little faster - it fails.“Well...,” I thought. The Chinese probably indicated Chinese amps in the specification. Well, okay, I have an excellent thick nichrome wire, now I’ll solder a piece of it on top of the shunt resistors (there are two 0.004 Ohm in parallel) and I will, if not happiness, then at least some improvement in the situation. There was no improvement. Even when I completely eliminated the shunt from the work, simply soldering the minus of the battery after it. That is, it’s not that there has been no improvement, but that there have been no changes at all.
And then I went online and discovered that there was no copyright for this rake - they had long been trodden by others. But somehow there was no solution in sight, except for the cardinal one - buy a board suitable specifically for screwdrivers.
And I decided to try to get to the root of the problem.
I dismissed the assumption that the overload protection was triggered during inrush currents, since even without the shunt nothing changed.
But still I looked with an oscilloscope at a homemade 0.077 ohm shunt between the batteries and the board - yes, PWM is visible, sharp consumption peaks with a frequency of approximately 4 kHz, 10-15 ms after the start of the peaks the board cuts off the load. But these peaks showed less than 15 amperes (based on the shunt resistance), so it’s definitely not a matter of current overload (as it turned out later, this is not entirely true). And the ceramic resistance of 1 Ohm did not cause a shutdown, but the current was also 15 amperes.
There was also the option of a short-term drawdown on the banks during startup, which triggered the overdischarge protection, and I went to see what was happening on the banks. Well, yes, horror is happening there - the peak drawdown is up to 2.3 volts on all banks, but it is very short - less than a millisecond, while the board promises to wait a hundred milliseconds before turning on the overdischarge protection. “The Chinese indicated Chinese milliseconds,” I thought and went to look at the voltage control circuit of the cans. It turned out that it contains RC filters that smooth out sudden changes (R=100 Ohm, C=3.3 uF). After these filters, already at the input of the microcircuits that control the banks, the drawdown was smaller - only up to 2.8 volts. By the way, here is the datasheet for the can control chips on this DW01B board -
According to the datasheet, the response time to overdischarge is also considerable - from 40 to 100 ms, which does not fit into the picture. But okay, there’s nothing more to assume, so I’ll change the resistance in the RC filters from 100 Ohms to 1 kOhm. This radically improved the picture at the input of the microcircuits; there were no more drawdowns of less than 3.2 volts. But it didn’t change the behavior of the screwdriver at all - a slightly sharper start - and then shut up.
“Let’s go with a simple logical move”©. Only these DW01B microcircuits, which control all discharge parameters, can cut off the load. And I looked at the control outputs of all four microcircuits with an oscilloscope. All four microcircuits do not make any attempts to disconnect the load when the screwdriver starts. And the control voltage disappears from the mosfets gates. Either mysticism or the Chinese have screwed up something in a simple circuit that should be between microcircuits and mosfets.
And I started reverse engineering this part of the board. With swearing and running from the microscope to the computer. 
Here's what we ended up with: 
In the green rectangle are the batteries themselves. In blue - the keys from the outputs of the protection chips, also nothing interesting, in a normal situation their outputs to R2, R10 are simply “hanging in the air”. The most interesting part is in the red square, which is where, as it turned out, the dog rummaged. I drew the mosfets one at a time for simplicity, the left one is responsible for discharging to the load, the right one is for the charge.
As far as I understand, the reason for the shutdown is in resistor R6. Through it, “iron” protection against current overload is organized due to the voltage drop on the mosfet itself. Moreover, this protection works like a trigger - as soon as the voltage at the base of VT1 begins to increase, it begins to reduce the voltage at the gate of VT4, from which it begins to reduce conductivity, the voltage drop across it increases, which leads to an even greater increase in the voltage at the base of VT1 and an avalanche-like a process leading to the complete opening of VT1 and, accordingly, the closing of VT4. Why does this happen when starting a screwdriver, when the current peaks do not even reach 15A, while a constant load of 15A works - I don’t know. Perhaps the capacitance of the circuit elements or the inductance of the load plays a role here.
To check, I first simulated this part of the circuit: 
And this is what I got from the results of her work: 
The X axis is time in milliseconds, the Y axis is voltage in volts.
On the bottom graph - the load is turned on (you don’t have to look at the numbers on Y, they are arbitrary, just up - the load is on, down - off). The load is a resistance of 1 ohm.
In the top graph, red is the load current, blue is the voltage at the mosfet gate. As you can see, the gate voltage (blue) decreases with each pulse of load current and eventually drops to zero, which means the load is turned off. And it is not restored even when the load stops trying to consume something (after 2 milliseconds). And although other mosfets with different parameters are used here, the picture is the same as in the BMS board - an attempt to start and shutdown in a matter of milliseconds.
Well, let’s take this as a working hypothesis and, armed with new knowledge, let’s try to chew on this piece of Chinese science :)
There are two options here:
1. Place a small capacitor in parallel with resistor R1, this is: 
The capacitor is 0.1 uF, according to the simulation it is possible even less, up to 1 nf.
The result of the simulation in this version: 
2. Remove resistor R6 altogether: 
The result of the simulation of this option: 
I tried both options - both work. In the second option, the screwdriver does not turn off under any circumstances - start, rotation is blocked - it turns (or tries with all its might). But somehow it’s not entirely peaceful to live with the protection turned off, although there is still protection against short circuits on the microcircuits.
With the first option, the screwdriver starts confidently with any pressure. I was able to achieve shutdown only when I started it at second speed (increased for drilling) with the chuck blocked. But even then it jerks quite strongly before turning off. At first speed I could not get it to turn off. I left this option for myself; I am completely satisfied with it.
There are even empty spaces for components on the board, and one of them seems to be specially designed for this capacitor. It was designed for the size of SMD 0603, so I soldered 0.1 uF here (circled it in red): 
RESULT
The board fully met expectations, although it was a surprise :)I don’t see the point in describing the pros and cons, it’s all in its parameters, I’ll point out only one advantage: a completely minor modification turns this board into a fully functional one with screwdrivers :)
PS: damn, it took me less time to remodel the screwdriver than it took me to write this review :)
ZZY: perhaps my comrades who are more experienced in power and analogue circuitry will correct me on something, I myself am a digital and analogue person through the roof :)
!
Now we, together with the author of the YouTube channel “Radio-Lab”, will assemble a battery for 4 banks from individual Li-ion 18650 batteries with a protection board, also known as BMS.
For the author's future projects, such a battery will be needed. On the Internet, he bought 8 of these Li-ion batteries from disassembly, like the Sanyo company.
The cans are used, but after running them on a charger, everything is fine, they will still work, the capacity is approximately 2100 mAh. We will use this inexpensive protection board with a built-in balancer (which is important); there is protection against overcharge and overdischarge.
The discharge current is stated to be up to 30A, for most tasks this is with a reserve. To increase the capacity, we will solder two batteries for each bank in parallel. But you can’t do this right away; you need to equalize the charge levels of the batteries so that they ruin each other. The easiest way is to fully charge all the batteries and then you can connect them in parallel. For charging, for example, you can use this simple charger based on a popular scarf.
Charged batteries can already be soldered in parallel; such batteries can be soldered, but this must be done quickly.
We will connect the batteries to each other using double-sided adhesive tape.
After this, we solder the batteries in pairs and get 4 separate banks for the future 4S battery. By connecting batteries in parallel we get an increase in capacity. For such assemblies, it is advisable to take batteries from the same batch.
Next, we connect the batteries so that we get a chain of alternating plus (+) and minus (-).
After this, we connect all the banks in series and in the end we get one battery.
The total voltage of the entire assembly is still 15.69 V, but for this battery to work for a long time, it needs to be protected. For this purpose we will use this BMS board.
How to connect it correctly can be seen in the figure above. First of all, we will connect the power + and - assemblies. We solder the power + and - to the battery and then, observing the polarity, we solder these wires to the B + and B- contacts on the board, everything is conveniently done.
Now it is very important to connect the wires correctly for balancing. The author pulled out the two outer wires of the balancing connector (they are also power + and -), they are already connected to the main tracks on the BMS board and are not needed in this case.
We connect the balancing connector and solder the balancing wires to the battery according to the diagram; the main thing is not to rush into anything complicated.
If this is done incorrectly, the balancer parts will begin to heat up and may fly off or burn. As a result, we got such a protected battery. Now in case of overcharging and overdischarging (which is important for lithium), the board will simply turn off the load and the battery will remain operational. There is also short circuit protection.
We solder wires to contacts P+ and P-, through which our battery will be charged and discharged.
And now, the battery is assembled, it turned out okay. Then you can try to charge it. To do this, you need to use a special power supply with a charging function for 4S Li-ion batteries. But the author decided to use a regular 19V power supply from a laptop.
You cannot connect it directly to the battery; you need to adjust the charging voltage and limit the charging current, but the BMS board cannot do this and works roughly like a relay to turn it on and off. To ensure that the battery is charged correctly, we will use this additional board for a step-down DC-DC converter.
It has the necessary algorithm for charging Li-ion batteries, with voltage adjustment and charge current limitation. The voltage of one charged battery is 4.2V, multiply by 4 and get the voltage of the entire charged assembly. According to calculations, this is 16.8V, but for normal operation of the BMS board, we will take the value of 4.25V and adjust the value at the converter output a little higher.
For convenience, the author has indicated where the voltage regulation is and where the current is. We set the voltage to 17.2V. For now, we will set the charging current to approximately 55mA, because the voltage of the cans is different and they need to be properly balanced.
The balancing current for this board is indicated in the description and is 60mA.
During balancing, these 8 resistors begin to heat up:
If the charging current is high, the balancer may not have time to convert excess charging energy into heat and balance the banks normally. We measure the voltage of each bank and you can see that they differ.
It is imperative to balance them, that is, to recharge those that are lower in voltage level so that everything is the same on all banks. Without balancing, some banks will be undercharged, and the entire assembly will not work to its full potential. Now, after all the settings, you can connect the step-down DC-DC converter board to the battery and start the charging process. For convenience, the author signed where + and where -. We connect everything and the blue LED lights up, that is, there is a current limit, only 55mA, which were previously configured, although the laptop power supply supplies more than 4A.
The voltage at the input is 19.6V, and at the output of the converter it will gradually increase to the level of the charged battery and at the end the blue LED will go out, the red LED will light up and the BMS board will turn off the battery.
After a few hours, we check the voltage levels on each bank.
You can see that they have leveled off and are approximately 4.2V, the battery is almost charged and balanced. Everything is working.
It is advisable to do the first battery charging cycle with a low current, and then you can set the current higher, because Usually, the further spread on the banks is not large and the balancer manages to equalize the voltages. After two cycles, the author adjusted the charge current to 2A and all banks were charged equally, now this battery can be used to power different devices. Let's connect a screwdriver for the test.
LiFePO4 batteries are compact and functional, lightweight, durable and optimal for any purpose. To protect against overdischarge and overcharge, to prevent prolonged excess of the discharge current, they are equipped with a BMS board, and for a capacity of over forty amperes they are supplemented with balancers. In terms of their advantages, the devices are significantly ahead of their “brothers”; they do not have a memory effect, are thermally and chemically stable, are non-toxic and are not subject to self-ignition. The minimum number of cycles, even with intensive use, is at least 2000 (up to 100% discharge), and with gentle use - about 8000 (if you do not discharge beyond 80%).
The assembly of a LiFePO4 battery consists of a series-parallel connection of the cells of the device. This requires electrical insulating materials, connectors, cable, charger, soldering iron or contact welding, LiFePO4 cells. The batteries are placed together, aligned, and glued together for convenience (according to a pre-selected pattern). After this, the technological patch is removed from each (using a solder or knife), jumpers, a balancer and a power wire are connected. To protect against short circuits, you should use heat shrink.
Connection diagram with symmetrical BMS board
BMS board connection diagram
LiFePO4: assembly according to the rules
It is important to remember that it is better to use cells from the same batch, otherwise, focus on their internal resistance. Not new products should be tested for capacity.
If the structure is created in series, then the voltage across the cells is summed up, the capacitance indicator remains unchanged. In this case, it is necessary to balance the elements, because each of them will have a different charge time.
A parallel connection does not require balancing of cells across parallels, it involves summing the capacitance, and the voltage parameter is unchanged.
The instructions for assembling a LiFePO4 battery are quite simple, but the process requires compliance with certain safety measures. All elements must be protected from mechanical shocks; safety glasses must be used for work. You cannot short-circuit terminals with different polarities (both on the batteries themselves and on the electrodes); it is recommended to tin them or solder them before installing the structure.
The connection is made:
- Spot welding.
- Soldering.
- Bolted connection.
The first option is suitable for self-assembly, it is effective and does not require mastery skills, the second must be done using a powerful soldering iron and when acting on the contacts for no longer than a couple of seconds, and the third is the most convenient way to assemble a LiFePO4 battery from cells that have a bolted connection.
Assembling a LiFePO4 battery is simple.
Views: 53069In recent years, so-called “smart” batteries, or in other words Smart batteries, have gained popularity. Batteries of this group are equipped with a microprocessor that is capable of not only exchanging data with the charger, but also regulating the operation of the batteries and informing the user about the degree of their performance. Batteries equipped with a specialized intelligent control system are widely used in a wide variety of technical electrical equipment, including electric vehicles. It is noteworthy that the group of smart batteries consists mainly of lithium-containing batteries, although sealed or ventilated lead-acid and nickel-cadmium batteries are also found among them.
Smart batteries are at least 25% more expensive than regular batteries. However, smart batteries differ not only in price, as most people assume, but also in the features of the control device included with them. The latter guarantees the identification of the type of batteries with the charger, monitors the temperature, voltage, current, and state of charge of the batteries. A significant portion of lithium-ion battery modules have a built-in monitoring and control system ( BMS), which is responsible for the condition of the batteries and manages them in such a way as to maximize the performance of the batteries under various conditions.
Let's take a closer look at what a battery with a BMS is. Smart batteries are batteries equipped with a special chip in which permanent and temporary data are programmed. Permanent data is programmed at the factory and cannot be changed: data regarding the BMS production series, its marking, compatibility with the type of battery, voltage, maximum and minimum voltage limits, temperature limits. Temporary data is data that is subject to periodic updating. These primarily include operational requirements and user data. As a rule, it is possible to connect the control and balancing system to a computer or controller in order to monitor the condition of the batteries and control their parameters. Some BMS models can be configured for different types of batteries (voltage levels, current values, capacity).
Battery management system (BMS) is an electronic system that controls the charge/discharge process of the battery, is responsible for the safety of its operation, monitors the condition of the battery, and evaluates secondary performance data.
BMS (Battery Management System)– this is an electronic board that is placed on the battery in order to control the process of its charge/discharge, monitor the condition of the battery and its elements, control the temperature, the number of charge/discharge cycles, and protect the components of the battery. The control and balancing system provides individual control of the voltage and resistance of each battery element, distributes currents between the components of the battery during the charging process, controls the discharge current, determines the loss of capacity from imbalance, and guarantees safe connection/disconnection of the load.
Based on the received data, the BMS performs cell charge balancing, protects the battery from short circuit, overcurrent, overcharge, overdischarge (high and excessively low voltage of each cell), overheating and hypothermia. The BMS functionality allows not only to improve the operation of batteries, but also to maximize their service life. When a critical condition of the battery is detected, the Battery Management System reacts accordingly by issuing a ban on the use of the battery in the electrical system - turning it off. Some BMS models provide the ability to maintain a register (record data) about the operation of the battery and then transfer it to a computer.
Lithium iron phosphate batteries (known as LiFePO4), which are significantly superior to other lithium-ion battery technologies in terms of safety, stability and performance, also come with BMS control circuits. The fact is that lithium iron phosphate batteries are sensitive to overcharging, as well as discharging below a certain voltage. In order to reduce the risk of damage to individual battery cells and failure of the battery as a whole, all LiFePO4 batteries are equipped with a special electronic balancing circuit - a battery management system (BMS).
The voltage on each of the cells combined into a lithium iron phosphate battery must be within certain limits and be equal to each other. The situation is such that ideally equal capacity of all cells that make up a single battery is a rather rare occurrence. Even a small difference of a couple of fractions of ampere-hours can provoke a further difference in the voltage level during the charging/discharging process. The difference in the charge/discharge level of the cells of a single LiFePO4 battery is quite dangerous, as it can destroy the battery.
When cells are connected in parallel, the voltage on each of them will be approximately equal: more charged elements will be able to pull out less charged ones. With a series connection, uniform distribution of charge between the cells does not occur, as a result of which some elements remain undercharged, while others are recharged. And even if the total voltage at the end of the charging process is close to ideal, due to even a slight overcharge of some cells in the battery, irreversible destructive processes will occur. During operation, the battery will not provide the required capacity, and due to uneven charge distribution, it will quickly become unusable. Cells with the lowest charge level will become a kind of “weak point” of the battery: they will quickly succumb to discharge, while battery cells with a larger capacity will only undergo a partial discharge cycle.
The balancing method allows you to avoid negative destructive processes in the battery. The BMS cell control and balancing system ensures that all cells receive equal voltage at the end of charging. When the charging process approaches the end, the BMS performs balancing by shunting the charged cells or transfers the energy of elements with a higher voltage to elements with a lower voltage. Unlike active balancing, with passive balancing, cells that have almost completely recharged their charge receive less current or are excluded from the charging process until all battery cells have the same voltage level. The Battery Management System (BMS) provides balancing, temperature control and other functions to maximize battery life.
Typically, stores sell ready-made prefabricated batteries with a BMS, but some stores and companies still provide the opportunity to purchase battery components separately. The Elektra company is one of them. Electra is the first company in Ukraine that decided to supply and create a market for battery cells for self-assembly and design of lithium iron phosphate batteries (LiFePO4) in our country. The main advantage of self-assembly of batteries from individual cells is the possibility of obtaining a prefabricated battery kit that is as close as possible to the user’s needs in terms of operating parameters and capacity. When purchasing components for assembling a LiFePO4 battery, it is important to pay attention not only to the compliance of the battery cells with each other, but also to look at the BMS parameters: voltage, discharge current, number of cells for which it is designed. The operation of a lithium iron phosphate battery also requires the use of only a charger that matches its type. Its voltage should be equal to the total voltage of the battery.
24v 36v 48v 60v
The main purposes of using BMS (BatteryManagementSystem) as a battery regulator:
Protection of battery cells and the entire battery from damage;
Increased battery life;
Maintaining the battery in a condition in which it will be possible to perform all the tasks assigned to it to the maximum extent possible.
FunctionsBMS (Battery Management System)
1. Monitoring the condition of the battery cells in terms of:
- voltage: total voltage, individual cell voltage, minimum and maximum cell voltage;
- temperatures: average temperature, electrolyte temperature, outlet temperature, temperature of individual battery cells, boards BMS(the electronic board is usually equipped with both internal temperature sensors that monitor the temperature of the control device itself, and external ones that are used to monitor the temperature of specific battery elements);
- charge and depth of discharge;
- charge/discharge currents;
- serviceability
The cell control and balancing system can store in memory such indicators as the number of charge/discharge cycles, maximum and minimum cell voltage, maximum and minimum charge and discharge current values. It is this data that allows you to determine the health status of the battery.
Improper charging is one of the most common causes of battery failure, so charge control is one of the main functions of the BMS microcontroller.
2. Intellectual computing. Based on the above points, BMS makes an assessment:
Maximum permissible charge current;
Maximum permissible discharge current;
The amount of energy supplied due to charging, or lost during discharge;
Internal cell resistance;
The total operating time of the battery during operation (total number of operating cycles).
3. Connected. The BMS can supply the above data to external control devices through wired or wireless communication.
4. Protective. The BMS protects the battery by preventing it from exceeding its safe operating limits. BMS guarantees the safety of connecting/disconnecting the load, flexible load control, protects the battery from:
Overcurrent;
Overvoltage (during charging);
Voltage drops below the permissible level (during discharge);
Overheating;
Hypothermia;
Current leaks.
BMS can prevent a process dangerous to the battery by directly influencing it or by sending an appropriate signal about the impossibility of subsequent use of the battery to the control device (controller). The intelligent monitoring system (BMS) disconnects the battery from the load or charger when at least one of the operating parameters goes beyond the permissible range.
5. Balancing. Balancing is a method of distributing charge evenly among all the cells of a battery, thereby maximizing the life of the battery.
BMS prevents excessive overcharging, undercharging and uneven discharge of individual battery cells:
By “shuffling” energy from the most charged cells to the less charged ones (active balancing);
By reducing the current flow to a nearly fully charged cell to a sufficiently low level while the less charged battery cells continue to receive normal charging current (bypass principle),
Providing modular charging process;
By regulating the output currents of the battery cells connected to an electrical device.
In order to protect the BMS board from the negative effects of moisture and dust, it is coated with a special epoxy sealant.
Batteries do not always have only one control and balancing system. Sometimes, instead of one BMS board connected via output wires to the battery and controller, several interconnected control electronic boards are used, each of which controls a certain number of cells and supplies output data to a single controller.
From a practical standpoint, BMSs can perform much more than just battery management. Sometimes this electronic system can take part in monitoring the operating mode parameters of an electric vehicle, and carry out appropriate actions to control its electrical power. If the battery is involved in the energy recovery system when braking an electric vehicle, then the BMS can also regulate the battery recharging process during deceleration and descent.